 <style>
        *
        {
            margin:0 auto;
            padding:0;
        }
        #all
        {
            height:100%;
            width:100%;
        }
        .odiv
        {
            background-image:url(image/3.jpg);
            background-size:cover;
            background-repeat:no-repeat;   
            height:100%;
            width:100%;       
        }
        #dl
        {
            position:absolute;
            color:white;
            background-color:black;
            left:35%;
            top:30%;
            border-top:4px solid black;
            border-radius:25px;
            padding:40px 0px 30px 30px;
            font-family:'Microsoft YaHei','Microsoft Uighur','Times New Roman';
            font-weight:500;
            line-height:40px;
        }
        #button2
        {
            width:100px;
            background-color:blue;
            color:black;
            height:40px;
            line-height:40px;
            border:0;
            border-radius:15px;
            font-family:'Microsoft YaHei','Microsoft Uighur','Times New Roman';
            font-weight:500;
        }
        #a2
        {
            color:blue;
        }


    </style>